The problems facing the government and the Labour party today - policy divisions, falling voter enthusiasm, rapidly shrinking membership - are political in their origin. They cannot be solved by rule changes and organisational tweaking of the kind now being prepared in Downing Street.

Ministers should instead be listening to the messages from this year's party conference, which voted against the creeping privatisation of the NHS and for more rights for employees. Or last year's, for that matter, which called for the return of the railways to public ownership and equal treatment for council housing. All these policies command majority support across Britain. Or they could listen to the message of this year's election campaign, in which Labour was only returned after a campaign in which the words "New Labour" were never uttered. Or the message of the thousands of loyal party members who have quit over the Iraq catastrophe.

But don't shoot the messenger. That is the danger, judging by the prime minister's speech to the Progress meeting last weekend. He proposed changes to Labour's constitution with the aim - under the now-traditional banner of "modernisation" - of further diluting trade-union input into the party's policy-making process and downgrading the role of conference itself.

A lot could be at stake. The truth is that Labour has seldom needed its affiliated trade unions more than it does today. Weakening that bond risks losing a vital link between the party and large numbers of its actual and former core voters: those who abandoned the party at the 2001 election and again this year, as well as those who stayed loyal.

Why are we threatened with an unnecessary bout of rule-mongering introspection? The short answer is that the government has started to lose conference votes. The present conference procedures, under which affiliated organisations and constituency parties have half the total vote each, have not been challenged for more than a decade. For most of that time the conference seldom defeated the platform and no one raised a peep about procedure. Now that the conference is finding its voice and urging more social justice and less inequality, Tony Blair wants to shift the goalposts.

This, of course, distracts attention from ministers' undemocratic habit of saying they will simply ignore any vote they do not agree with - and from the substance of the policy arguments.

In fact, the unions and the Labour conference as a whole are closer to public opinion than the government on the key issues in dispute between us. And in the Labour party it is far from being the trade unions alone who want a change of direction. Nearly 40% of constituency delegates at Labour's conference in Brighton supported the union position on the right to solidarity action and against NHS privatisation - the highest figures on contested issues for years.

Mr Blair has told the unions to get into the "real world". That is the world in which Labour's vote fell to an unprecedented low for a re-elected government this year, with millions of core Labour voters - and most young people - staying at home. The idea that this will be reversed by tinkering with party procedures is fanciful. The unions - which worked hard to help Labour win - are a genuine democratic link with many of those missing voters and their communities. A Labour party with no place for working-class collectivism would be a Labour party no longer.

And who would replace the unions in Labour's democracy? The last time this was debated in the party, early in the 1990s, the unions were to be replaced by a mass individual membership, scheduled to be a million strong by now. But Labour's membership is now 200,000 at most and falling. Half the members have been lost in the last seven years, a fact which cannot be disentangled from disenchantment with government policy - including the very issues on which Labour's sovereign body is now urging ministers to think again.

The constituency parties also seem to be in crisis. Only 400 out of more than 600 sent a delegate to this year's conference. Constituency delegates therefore represented maybe 120,000 individual members at most. As a lifelong party member I do not rejoice at this for a second. Any plan to revive Labour must include steps to reverse this membership decline. But that will take time - and a change in government policy. In the here and now, the affiliated unions - hundreds of thousands of whose members recently voted to maintain political funds which largely go to sustain the Labour party - are an indispensable connection to ordinary Labour voters.

Labour is losing members and voters, and the government is losing conference votes, for much the same reasons. Most Labour people oppose neoliberal, deregulating and privatising economic policies and a neo-imperialist foreign policy. Like the majority of the British people, they want a narrowing of the gap between rich and poor, public control of public services and an independent foreign policy. This is the centre ground in British politics today. Taking these concerns seriously (as the government has this week on public-sector pensions) is the route to renewal - if not for the prime minister, then for his successor.

· Tony Woodley is general secretary of the Transport and General Workers' Union